The present invention relates to the measurement of surface topology of semiconductor wafers prior to their fabrication by semiconductor manufacturers into various micro circuits and other similar devices.
Semiconductor wafers are expensive real estate in that the manufacturers of semiconductor products need to know the quality of the surface area of the wafers, which can be as large as 300 cm across, before committing time, equipment and materials to process them into finished semiconductor products. If there is a sufficient perturbation in the surface profile of a portion of a semiconductor which could prevent its being processed into a finished product, that information needs to be known before the manufacturer proceeds so that that portion can be eliminated from processing. This problem is particularly severe in the edge areas of semiconductors where there tends to be a slope roll-off so that traditional thickness measurements by themselves are unlikely to reveal the presence of all or many bumps that affect the processing of finished semiconductor products.
Current processing and sensing techniques for a wafer surface profile are inadequate to accurately reveal the presence of a bump which exists as a significant variation from the local surface profile. Present techniques use a proximity probe which may, in fact, be a laser interferometer, to measure thickness of a wafer. This information is presently processed to provide a curvature profile by taking the second derivative of the curve representing data obtained by current probing technologies.